As electronics and semiconductor technology are rapidly developed, information communication devices are required to be multi-functional, miniaturized, and broadband with a high speed. As an operation speed of high speed digital system increases and a clock frequency is at several GHz, simultaneous switching noise (SSN) is generated in an on/off chip, a multi-layer printed circuit board (PCB) or a package structure and is problematic. The SSN can cause the significant problems with signal/power integrity (SI/PI), as well as electromagnetic interference (EMI), exciting the cavity resonance modes within parallel plate waveguide-type power/ground planes.
FIG. 1 is a diagram illustrating a current flow path, and SSN and EMI generation mechanism in a multilayer PCB or package structure using a high speed signal.
In the multi-layer PCB or package structure, a power distribution network (PDN) formed of a pair of power plane and ground plane is embedded within its multilayer structure. This PDN structure embedded in multilayer structure has a form of a parallel plate waveguide. FIG. 1 shows an example of a multi-layer PCB or package structure 100 using a high speed signal in which a layout of respective layers such as a signal layer, the power plane 140 and the ground plane 130 and an integrated circuit (IC) device 110 performing the fast switching operation, signal flow paths 180 and 185, and generation mechanism of SSN 195 and EMI 190 are illustrated.
Generally, it is known that simultaneous switching noise (SSN) 195 is the most severe noise in the multi-layer PCB or package structure 100. The SSN 195 is also called delta-I noise or ground bounce noise (GBN). This noise is generated between the power plane 140 and the ground plane 130 due to time-varying current that rapidly varies in a high-speed digital circuit. The SSN 195 may affect SI/PI of a circuit and cause radiation of unwanted electromagnetic-wave 190 at edges of the multi-layer PCB or package structure 100. Accordingly, suppression of the SSN 195 is a key concern in a high-speed digital computer system operating at a low voltage level with a high clock frequency.
A recent high-speed digital system has hundreds of simultaneously switched gates. When high speed current flows through a via 131, the via 131 through which the fast current flows functions as an antenna and the noises generated from via are propagated through the power distribution network, which has a form of parallel plate waveguide structure, formed of the power plane 140 and ground plane 130. And then the propagated noises may affect an adjacent signal lines or devices, finally causing the SI/PI problem. Further, the noises arrive at an edge of the structure radiates out unwanted electromagnetic-wave 195. That is, the unwanted electromagnetic-wave 195 is propagated to the entire PCB 100 through a dielectric layer 170 by resonance of parallel conductor plates and then emitted to the exterior at the edges of the PCB 100. The SSN 195 is inductive noise generated in a high-speed digital system due to rapid changes in current when output terminals of the digital gates are simultaneously switched. It is difficult to measure an amount of the SSN 195 since the SSN 195 depends on a form of the multi-layer PCB or package structure 100 or the current flow paths 180 and 185. The noise voltage due to the SSN may be simply expressed by Equation 1:
                              V          noise                =                              N            ·                          L              eq                                ⁢                                    ⅆ              i                                      ⅆ              t                                                          [                  Equation          ⁢                                          ⁢          1                ]            wherein Vnoise denotes a noise voltage generated due to SSN, N denotes the number of simultaneously switched gates, and Leq denotes the effective inductance of the power distribution network.
Conventional techniques for suppressing SSN in a multi-layer PCB or package structure include the application of a decoupling capacitor (DeCap), an embedded thin film capacitor, a stitching via, and ground filling in the multi-layer PCB.
The decoupling capacitor is a decoupling device having large capacitance and connected between the power plane and the ground plane. Researches for removing a parasite inductance component of a power plane and supplying a stable power using the decoupling capacitor has been proceeded steadily. However, a decoupling capacitor mounted in the multi-layer PCB may increase a production cost, make it difficult to dispose other devices in a limited space of the PCB, and cause another parallel resonance frequency due to its parasite inductance. In addition, the decoupling capacitor has too low operation frequency of hundreds of MHz to effectively suppress the SSN in a GHz band that is problematic in high-speed systems.
The embedded thin film capacitor has been developed to reduce the parasite inductance component of the decoupling capacitor. The embedded thin film capacitor is manufactured by disposing a high dielectric material, as a thin film, between a power plane and a ground plane. The embedded capacitor can provide a better SSN suppression characteristic in a relatively high frequency band than the decoupling capacitor. However, the embedded capacitor requires a high dielectric thin film material and additional process in order to effectively suppress the SSN in a GHz band.
In addition, the stitching via, the ground filling and the like locally operates in only a limited region of a PCB/package structure and exhibits a noise suppression characteristic in only a narrow band at GHz frequency or less. Thus, these approaches have small effects in current GHz-class high-speed systems, as known.
Accordingly, electromagnetic control structures having electromagnetic-wave suppression characteristic in a specific frequency band, such as an Artificial Magnetic Conductor (AMC), a High Impedance Surface (HIS), and an electromagnetic band-gap (EBG), have been proposed to solve a noise problem in the GHz band.
The electromagnetic control structures have a periodic structure in which certain pattern unit cells are formed adjacent to one another. The electromagnetic control structures including the electromagnetic band-gap (EBG) structure have a high impedance characteristic in a specific frequency band, and accordingly a broadband rejection characteristic to surface current. In a multi-layer PCB or package structure, the EBG effectively suppresses SSN, improves SI/PI and EMI, and has a better frequency selection characteristic, compared to the decoupling capacitor and the embedded thin film capacitor. However, such an EBG structure initially proposed as a mushroom shape of a two-layer structure has problems of complex process of forming a blind via and high production cost.
Meanwhile, in order to solve these problems, an EBG structure having a periodic pattern provided only on a single surface has been proposed. The EBG structure provides process convenience and exhibits a noise reduction characteristic in a power distribution network (PDN) circuit in a parallel-plate waveguide form, but affects a high speed signal line to thereby degrade an SI characteristic.